Panama’s Worst Drought Hints at the Future of Its Canal

A severe drought in Panama has resulted in lower water levels in the Panama Canal, forcing some shippers to limit the amount of cargo their largest ships carry so they can safely navigate the waterway.

“The last five months have been the driest dry season in the history of the canal,” said Carlos Vargas, the Panama Canal Authority’s executive vice president for environment, water and energy.

The canal — an engineering masterwork that provides a shortcut between the Atlantic and Pacific — handles about 5 percent of maritime trade. Any hiccup in its operation can ripple through the global economy and affect the United States, the origin or destination for much of the canal’s traffic. And those problems may become more commonplace as the climate changes.

Earlier this year, the authority imposed draft limits on ships, forcing some to lighten their loads to ride higher in the water so they will not run aground.

Although the dry season has ended and rains have returned, some restrictions will remain through the summer, Mr. Vargas said. Such restrictions may have to be imposed more frequently if, as scientists expect, climate change leads to more extreme storms and dry periods.

The drought is linked to an El Niño that developed early this year and is expected to continue into the fall. During an El Niño, warmer-than-normal surface waters in the equatorial Pacific can affect weather patterns in many parts of the world, including rainfall in Central America. El Niño events occur every two to seven years, on average, and have been noticed for centuries. They have led to canal restrictions in the past.

Already, four of the most intense storms and several of the worst droughts since the canal opened 105 years ago have occurred in the past decade, said Robert F. Stallard, a hydrologist with the United States Geological Survey and the Smithsonian Tropical Research Institute who has studied water issues in Panama for decades.

“Planning for more extreme weather in the future is the way things have to go,” Dr. Stallard said.

The authority imposed the limits in February, as the drought took hold and levels in the two lakes that supply water to the canal began to fall. The limits affected only very large ships using the canal’s newest locks, which opened in 2016. An average of about seven ships a day use those locks.

The canal authority posts the restrictions well in advance, so shippers can calculate loads that will enable their ships to transit the 50-mile canal. Otherwise excess cargo has to be off-loaded in Panama.

Since the February announcement, the maximum allowable draft has been reduced five times. As of May 28 the maximum will be 43 feet, seven feet lower than usual.

Mr. Vargas said that as of that date smaller ships that use the canal’s old locks will also be affected, as the maximum allowable draft for those locks will fall from 39 and a half feet to 38 and a half. About 25 ships use the old locks every day.

Because canal tariffs are based partly on cargo loads, the limits have so far cost the canal authority about $15 million, a relatively small amount when compared with overall revenues of more than $2 billion a year.

Mr. Vargas said the restrictions will be lifted gradually, probably beginning in June. By mid-September, he said, even ships with the deepest drafts should be able to use the waterway without having to reduce their cargo.

Draft restrictions have been imposed before, during previous El Niño years, and have sometimes caused greater revenue losses. Dr. Stallard said the impact of the drought this year was reduced in part because of heavy rains last fall.

Managing water has always been a critical part of canal operations, but became even more important with the construction of the larger locks. Each time a ship transits the canal about 50 million gallons of fresh water are lost through the locks to the oceans.

That water comes from the two artificial lakes, Gatún — through which ships pass as part of the canal — and Alajuela. The lakes also provide water for much of Panama’s growing population.

Canal operators try to store enough water in the rainy season to operate the canal fully during the dry season. As this year has shown, that is not always possible. Even in normal years, saving water is a priority — the new locks, for example, have special basins that conserve about half the water used each time a ship passes through the canal.

But the rainy season has its own challenges. In December 2010, torrential rains caused the lakes to overflow; the resulting flooding forced the canal to be closed for a day. Too much water inundating the system can also damage locks and other infrastructure.

Mr. Vargas said the authority has a team of meteorologists, scientists and engineers who forecast and plan how to handle water extremes, and their skills will be used even more as the climate changes.

As for the long-term threat to the canal, Mr. Vargas said the solution is more water. “We have no doubt that we need to build more reservoirs,” he said. “We think they are the most effective way to mitigate climate change.”

But adding new reservoirs would be a costly and lengthy undertaking. There is no more water available from the Chagres River watershed, which supplies Gatún and Alajuela. New water would have to come from watersheds that are farther from the canal, requiring the construction of tunnels as well as dams.